1. Field of the Invention
The present invention relates to a rotor of a BLDC motor, and more particularly to, a rotor of a BLDC motor which can improve a torque of the motor by minimizing flux leakage of magnets.
2. Description of the Background Art
In general, BLDC motors are classified into surface mounted magnet type motors and interior permanent magnet type motors according to structure of a magnetic circuit.
A torque of the surface mounted magnet type motor is a magnet torque generated by interactions between a flux generated in magnets and a winding current of a stator. A torque of the interior permanent magnet type motor is a sum of a torque generated by overlapping of a reluctance torque generated by different magnetic resistances by relative positions of a magnetic pole by a current of a stator and a magnetic pole by magnets of a rotor, and the torque of the surface mounted magnet type motor.
FIG. 1 is a perspective view illustrating a disassembled state of a conventional BLDC motor, and FIG. 2 is a plane view illustrating the conventional BLDC motor.
The conventional BLDC motor includes a stator 102 fixed to a casing of a washing machine for receiving power, and a rotor 104 disposed on the outer circumference of the stator 102 with a predetermined air gap, connected to a laundry sink of the washing machine, and rotated by interactions with the stator 102 when power is applied to the stator 102.
Here, the stator 102 has a stator core 106 formed by stacking a plurality of circular sheets, teeth 108 mounted on the outer circumference of the stator core 106 in the radial direction at predetermined intervals, and coils 110 coiled around each of the teeth 108 for receiving power.
The rotor 104 includes a rotor frame 120 having a housing space of the stator 102 and having back yokes that are flux paths on its outer circumference, and a plurality of magnets 122 disposed on the inner circumference of the rotor frame 120.
The magnets 122 are formed in a circular arc shape, magnetized in the radial direction, and arranged on the inner circumference of the rotor frame 120 in the circumferential direction.
The operation of the conventional BLDC motor will now be explained.
When power is applied to the coils 110, a torque is generated by interactions between a flux formed by the magnets 122 of the rotor 104 and a flux formed by the coils 110 of the stator 102, for rotating the magnets 122. Therefore, the rotor frame 120 to which the magnets 122 are fixed is also rotated.
As shown in FIG. 3, the conventional BLDC motor shows flux distributions by relative positions of the rotor 104. There are no magnetic resistance differences by relative positions of a magnetic pole by the current applied to the coils 110 of the stator 102 and a magnetic pole by the magnetic force of the magnets 122.
In the conventional BLDC motor, to increase a counter electromotive force, a stack length of the rotor 104 is set to be longer than a stack length of the stator 102, which is generally called an overhang. The overhang improves the counter electromotive force by increasing the flux of the magnets 122 interlinked with the coils 110 of the stator 102 by a predetermined amount. In this case, the counter electromotive force increases by the overhang of the rotor 104. However, the counter electromotive force does not increase but maintains the same level over a predetermined overhang. Accordingly, it is limitative to increase the torque of the motor.
FIG. 4 is a graph showing a flux density by an overhang length in the conventional BLDC motor.
As depicted in FIG. 4, in the conventional BLDC motor, when the overhang of the rotor 104 increases, the flux density of the magnets 122 gradually increases. When the overhang of the rotor 104 reaches about 6 mm, the flux density of the magnets 122 does not increase but maintains the same level.